1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to a method of locating a mobile terminal.
2. Description of the Related Art
The main feature of mobile communication systems is mobility. While existing wired communication systems are limited in mobility over a wired network, the mobility limitations are overcome over a wireless network in the mobile communication systems. The mobility is ensured by use of a mobile terminal. In a cellular mobile communication system, a mobile terminal detects a reference cell having the strongest pilot channel signal by continuously searching neighbor cells and demodulates a signal having the best quality among signals received in different paths from the reference cell. For path demodulation, the mobile terminal performs neighbor cell search continuously. The neighbor cell search is also needed at a handoff.
In an existing synchronous mobile communication system, the timing offsets of base stations are used in cell search. That is, all base stations synchronize their timings to a clock signal received from one GPS (Global Positioning System) at predetermined different time intervals. A mobile terminal detects the timing of a neighbor cell by comparing the timing offset of the neighbor cell received from a network and its current searcher timing. The mobile terminal updates cell search results by measuring the energy (reception power level) of the neighbor cell using the detected timing. If the measured energy is higher than that of a signal from its serving base station, the mobile terminal performs a handoff. The use of timing information about a neighbor cell facilitates a search for the neighbor cell by window cell search in the synchronous system.
Meanwhile, with asynchronous deployment, since Node Bs do not have unique timing offsets, the above cell search method is not valid in UMTS.